This invention relates generally to the operation of fast acting nuclear reactor control devices and more particularly, to a device for providing primary drive to a safety control rod in a nuclear reactor to provide for control of the nuclear reaction, and as conditions warrant, for shutdown of the nuclear reactor.
Nuclear reactors typically employ control rods which are inserted into the core of the reactor to control the level of the nuclear reaction. Control rods are commonly used during normal operation of the reactor to maintain a desired level of neutron flux in the core, and additionally, some of the safety rods provide a means for shutting down the reactor in emergency situations ("SCRAM"), or normal shutdown All such rods have a neutron absorbing portion containing a substance, such as hafnium, to control the flow of neutrons. Movement of the rods in or out of the core controls the nuclear reaction. When it is necessary to shut down the reactor during emergency situations the entire neutron absorbing portion of the safety control rod must be inserted as rapidly as possible into the reactor core.
Various fast acting nuclear reactor control devices have been employed in attempting to provide a reactor control system. Most nuclear reactor facilities use spring drives held in a strained position. For example, one design employs a compression spring and a recirculating ball lead screw arrangement. The spring provides torque to the drive system mainshaft by driving the ball lead screw. This design has several limitations. The spring provides a decreasing torque resulting in less overall energy input and requires a high retaining torque. This encumbers the fast release capabilities of an electrical clutch also employed in this design, because high currents are required in the clutch to resist this torque. Another imitation is that the highly loaded lead screw is prone to galling and lacks efficiency. Additionally, the spring and ball screw SCRAM-assist system provides torque only during about the first one-third of the safety control rod's downward stroke as it is positioned in the reactor core. The remainder of the downward stroke is effected by the weight of the rod under the influence of gravity, and water pressure if so configured.
Accordingly, it is an object of the present invention to overcome the inefficiencies of present nuclear reactor safety control rod drive units to improve the safety and reliability of nuclear reactor operation.
It is a further object of the present invention to provide a fast acting nuclear reactor control device which improves the safety performance and reliability of nuclear reactor operation.
Another object of the present invention is to provide a nuclear reactor control device which better maintains power and force to compel safety-rod insertion over the full length of the control rod.
Yet another object of the present invention is to provide a nuclear reactor control device which provides for easy adjustment and control of the control rod.
An additional object of the present invention is to provide a nuclear reactor control device which allows the safety control rod system to freely travel toward a safe position in the event of a partial drive system failure.